The present invention relates to a zoom lens, particularly to a zoom lens preferably used in a compact image sensor having a zoom ratio of three used in a digital still camera or video camera.
The widespread use of a personal computer in recent years has increased the frequency of handling image data through the use of the personal computer. It has also increased the demands for a digital still camera and others for capturing the image data. The spread of such digital still cameras has required the advent of a less expensive digital still camera. It has become essential to achieve a further cost reduction than the image pickup optical system. In the meantime, the number of pixels of the photoelectric conversion device tends to increase every year, the optical pickup system is required to provide higher performances. This trend requires the industry to meet the mutually conflicting requirements of cost reduction and performance upgrading. An example of the CCD zoom lens for meeting such a demand is found in the following Japanese Patent Application Publication Nos. 2002-372667 and 2003-50352.
The zoom lens proposed in the Japanese Patent Application Publication No. 2002-372667 achieves cost reduction by using a plastic lens in the second group. However, the proportion of the plastic lenses used in the constituent lenses is insufficient to achieve cost reduction. In the meantime, the zoom lens proposed in the Japanese Patent Application Publication No. 2003-50352 achieves cost reduction by using plastic lenses in various groups. However, the zoom ratio is as small as 2 through 2.5, and there is still room for improvement in the optical specifications as a zoom lens in recent years.